Collaborative Research: Exploring the Magmatic, Crustal, and Conduit Conditions Required for Mafic, Plinian Volcanism

低硅质基性岩浆是地球上最常见的喷发岩浆。因为它们的粘度很低，所以通常会形成熔岩流或微弱的爆炸性喷发。然而，岩浆构成的火山可以产生更强烈的普林尼式喷发，能够将火山灰分散到数千平方公里的范围内，并产生致命的、改变景观的火山灰流，从源头传播数十公里。尽管它们有潜在的影响，但产生岩浆和普林尼火山爆发的机制尚不清楚。该项目将通过限制此类火山爆发的原因和后果而造福社会，这对数百万生活在包括美国目前活跃的基拉韦厄火山在内的基拉韦厄火山中心的危险中的人们具有全球性影响。两名博伊西州立大学（BSU）的博士生将由团队中的五名参与科学家进行培训，在促进教学、培训和学习的同时推进发现和理解。来自康塞普西翁大学（智利）的地球科学本科学生将被纳入实地工作和研究，扩大代表性不足群体的参与。研究小组的成果和经验将在BSU岩浆和火山研究小组的Facebook页面上通过一系列博客文章和简短的视频分享，这些视频记录了与该项目相关的发现的关键要素。最后，调查人员和学生将把在智利工作的样本、故事、图像和视频纳入当地和区域推广工作。该项目以智利Llaima火山的13.4 ka （~12 km3 DRE）和~12.6 ka （~1 km3 DRE）岩浆喷发为研究对象，这些火山喷发产生了广泛的火山灰流沉积物，在火山周围呈放射状分布。喷发规模的差异使我们能够研究促进大体积、破火山口形成的基性火山喷发与小体积的普林尼亚基性火山喷发的过程。包括岩石学、地球化学、物理火山学、减压实验和流变学实验在内的一整套不同但互补的方法，使研究团队能够解决岩浆和地壳条件促进和触发基性普林尼火山爆发的广泛基础研究问题。更具体地说，空间和地层限制的岩石学和地球化学研究将使我们能够调查喷发期间和之前的岩浆条件，例如岩浆的成分变化以及岩浆室温度、压力和气体含量的变化。在这些条件下建立可变性将允许重建岩浆管道系统。所有方法的组合都用于限制管道条件，这些条件会促进基性熔体的高爆炸性，包括岩浆上升速率和脱气之间的相互作用，以及防止气体损失的岩浆流变学变化，从而促进更高的爆炸性。这项工作的结果将对理解扩展到世界各地的岩浆中心的爆炸性岩浆喷发过程产生影响，包括大体积和小体积的岩浆，普林尼火山喷发。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Low-silica 'mafic' magmas are the most common magmas to erupt on Earth. Because their viscosity is low, they usually form lava flows or weak explosive eruptions. However, mafic-composition volcanoes can produce much stronger, Plinian-style eruptions capable of dispersing ash fall over thousands of square kilometers, and producing deadly, landscape-altering ash flows that travel tens of kilometers from source. Despite their potential impact, the mechanisms responsible for generating mafic, Plinian eruptions are not understood. This project will benefit society by constraining the causes and consequences of such eruptions, which has global implications for the millions of people living at risk from mafic volcanic centers including the currently active Kilauea volcano in the USA. Two Boise State University (BSU) PhD students will be trained by the five participating scientists on the team, advancing discovery and understanding while promoting teaching, training, and learning. Undergraduate geoscience students from the Universidad de Concepcion (Chile) will be included in the field work and research, broadening participation of under-represented groups. The results and experience of the research team will be shared on the BSU magmatic and volcanic studies group Facebook page through a series of blog post and short videos of our field work that document the key elements of discovery associated with the project. Finally, the investigators and students will incorporate samples, stories, images and videos from the work in Chile into local and regional outreach efforts.This project targets the 13.4_ka (~12 km3 DRE) and ~12.6 ka (1 km3 DRE) mafic eruptions at Volcan Llaima, Chile, which produced extensive ash flow deposits found radially around the volcano. The difference in eruption sizes permits investigation of processes that promote large-volume, caldera forming mafic eruptions versus smaller volume Plinian mafic eruptions. A full suite of diverse but complimentary methods, including petrology, geochemistry, physical volcanology, decompression experiments, and rheology experiments, allows the research team to address the broad, fundamental research question of what magmatic and crustal conditions promote and trigger mafic, Plinian eruptions. More specifically, spatially and stratigraphically constrained petrologic and geochemical studies will allow us to investigate magmatic conditions during and prior to eruption, such as compositional variability of the magma and changes in chamber temperatures, pressures, and gas content. Establishing variability in these conditions will permit reconstruction of the magma plumbing system. A combination of all methods are used to constrain conduit conditions that promote high explosivity for mafic melts, including the interplay between ascent rate and degassing of the magma, as well as changes in magma rheology that prevent gas loss, promoting higher explosivity. The results of this work will have implications for understanding explosive mafic eruptive processes that extend to mafic centers worldwide, including both large-volume and small-volume mafic, Plinian eruptions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.